The present invention relates to a resin-encapsulation method for electronic parts by a stencil printing, and a stencil to be used for the method.
In the prior art, it has been widely and generally executed to resin-encapsulate electronic parts mounted on a substrate by a stencil printing. As the electronic parts grow thinner and lighter, however, the demand is intensified day by day for finishing the thickness of the resin-encapsulated layer homogeneously.
As disclosed in Japanese unexamined patent publication (Kokai) No. 11-74294, therefore, at the squeegee movement terminal side end portions of the resin filling openings in a stencil, it has been proposed (as referred to FIG. 4) to form recesses for reserving the excess resin corresponding to a protuberance of the resin, as caused at the time of the forced fill of a encapsulation resin by a squeegee, thereby to prevent the heterogeneous thickness of the resin-encapsulated layer or to homogenize the thickness of the resin-encapsulated layer.
According to the aforementioned prior art method for forming the recesses, however, the stencil printing is performed several times by moving the squeegee back and forth thereby to force and fill a predetermined amount of resin in the resin filling openings of the stencil (as will be called the xe2x80x9cfilling printingxe2x80x9d). After the final finish printing, the lower substrate carrying the electronic parts in the resin-encapsulated figure is then moved downward of and separated from the upper stencil on the stationary side. Then, the so-called xe2x80x9cstringinessxe2x80x9d is caused, as shown in FIG. 4(a), mainly by the excessive resin 5 which is left in the recess 10. When the substrate 1 is further moved downward, moreover, the resultant stringy resin is cut (as referred to FIG. 4(b)).
As a result, the thick and long stringy resin, as cut, on the substrate side may fall down either on the resin layer encapsulating the electronic parts or on the substrate so that its encapsulated figure is deformed (as referred to FIGS. 4(c) and 4(d)). This raises quality problems that especially the flatness of the resin-encapsulated layer drops to deteriorate the finished figure (or appearance) of the resin encapsulation, and that the resin sticks to such a portion on the substrate as should be cleared of the resin.
As the electronic parts are sequentially resin-encapsulated, on the other hand, the excess resin left in the aforementioned recess will be modified in their properties as the time elapses. As the case may be, the modified residual resin (e.g., a solidified resin lump) may migrate into a new resin to form a coarse surface. This point deteriorates the finished figure (or appearance) of the resin encapsulation and is not preferable for the quality.
The present invention has been conceived by noting those defects and contemplates to improve the appearance quality of the resin encapsulation and to homogenize the thickness of the resin-encapsulated layer.
In order to achieve the above-specified object, according to the present invention, there is provided a resin-encapsulation method for electronic parts by a stencil printing, in which a resin filling opening in a stencil is filled with a resin while a squeegee is being moved over the stencil. In the resin-encapsulation method, elevation control of the squeegee is so made in a finish printing process at a position close to an end portion of the resin filling opening on a squeegee movement terminal side as to scrape the excess of the filing resin out of the resin filling opening.
In the above-specified electronic parts resin-encapsulation method, the stencil having the resin scrape promoting recess connected to the end portion of the resin filling opening on the squeegee movement terminal side may be used, in the finish printing process, to bring the squeegee downward into the resin scrape promoting recess. Specifically, it is preferred that the resin-encapsulation stencil is provided with the resin scrape promoting recess connected to an end portion of the resin filling opening. It is preferred that the resin scrape promoting recess is connected to a plurality of resin filling openings, and is desired that the resin scrape promoting recess is longer than the width of the squeegee.